In radio frequency identification (“RFID”) technologies, the situation that one card reader needs to read multiple cards simultaneously is often encountered. How to implement an anti-collision mechanism under such a multi-card collision is one of the problems to be resolved in RFID technologies.
Currently, the anti-collision mechanism adopted by most RFID technologies is as follows: compare the user identification codes (UIDs) of the cards from a low bit to a high bit, and record the bit position at which a collision (i.e., conflict) occurs among the UIDs of the multiple cards. Since the UID of each card is unique globally, it is possible to differentiate the cards with different UIDs and use the cards to perform different data transactions, after bit-by-bit comparison of the UIDs. When this mechanism is used, if the UIDs of two cards to be read are different at high bits but identical at low bits, and then it surely costs much more time, by using the bit-by-bit comparison method, to identify the bit position at which the UIDs of the two cards are different. Therefore, in actual applications, this card-reading method will certainly cause a whole transaction to become very slow due to the long card-reading time.